This invention relates to a position measuring method for measuring a position of a node having a radio transmitting function, a node position measuring system using the method, and an access point (AP) used as a base station in the node position measuring system.
As a representative conventional node position measuring method, there has been available a method of measuring a position by using a signal from a satellite such as a GPS.
As another node position measuring method, there has been available a method of receiving signals sent from several base stations by a node and calculating a position of the node based on a reception timing difference of the signals.
Specifically, regarding a cellular telephone system, there has been proposed a method of calculating reception timing differences of signals sent from base stations to a mobile terminal (propagation time differences T1−T2 and T3−T2 of signals from the base stations to the mobile terminal), multiplying the propagation time differences by a light velocity, to calculate propagation distance differences of signals from the mobile terminal to the base stations, which is expressed by the following equations:D1−D2=c(T1−T2); andD3−D2=c(T3−T2),to thereby calculate a position of the moving terminal (for example, refer to JP 07-181242 A).
Furthermore, regarding a radio LAN system, there has been proposed a method of calculating a reception timing difference of signals sent from a node and received by base stations (reception timing difference Ti−T1 between the base stations), multiplying the reception timing difference by a light velocity, to calculate a propagation distance difference of the signals from the node to the base stations, which is expressed by the following equation:{|P−Pi|−|P−P1|}=c(Ti−T1), i=2, . . . , n,to thereby calculate a position of the node (for example, refer to Atsushi Ogino and five others, “Wireless LAN Access System (1) Study of Position Detecting System”, 2003. General Assembly Lecture Thesis Collection, The Institute of Electronics, Information and Communication Engineers, B-5-203, p. 662).
Also, there has been proposed a hyperbolic method of calculating a position of a node by using a hyperbolic curve (for example, refer to JP 2003-189353 A).